The present invention relates to coatings containing an additive for promoting adhesion.
As used herein, xe2x80x9cautomotive refinishxe2x80x9d refers to compositions and processes used in the repair of a damaged automotive finish, usually an OEM provided finish. Refinish operations may involve the repair of one or more outer coating layers, the repair or replacement of entire automotive body components, or a combination of both. The terms xe2x80x9crefinish coatingxe2x80x9d or xe2x80x9crepair coatingxe2x80x9d may be used interchangeably.
Automotive refinishers must be prepared to paint a wide variety of materials. Examples of commonly encountered materials are one or more previously applied coatings, plastic substrates such as RIM, SMC and the like, and metal substrates such as aluminum, galvanized steel, and cold rolled steel. Bare metal and plastic substrates are often exposed as a result of the removal of the previously applied coating layers containing and/or surrounding the defect area. However, it is often difficult to obtain adequate adhesion of refinish coatings applied directly to exposed bare substrates.
Among the many factors influencing the degree of refinish coating/substrate adhesion are the type of exposed substrate, the presence or absence of adhesion promoting pretreatments and/or primers, the size of the exposed area to be repaired, and whether previously applied xe2x80x9canchoringxe2x80x9d coating layers surround the exposed repair area.
For example, refinish adhesion is particularly challenging when the exposed substrate is a bare metal such as galvanized iron or steel, aluminum or cold rolled steel. It is especially hard to obtain adequate refinish adhesion to galvanized iron. xe2x80x9cGalvanized iron or steelxe2x80x9d as used herein refers to iron or steel coated with zinc. xe2x80x9cSteelxe2x80x9d as used herein refers to alloys of iron with carbon or metals such as manganese, nickel, copper, chromium, molybdenum, vanadium, tungsten and cobalt.
Refinish operations have traditionally used adhesion pretreatments to overcome the adhesion problems associated with the coating of bare metal substrates. Pretreatment as used herein may refer to either mechanical or chemical alterations of the bare metal substrate. Mechanical alterations used to obtain improved adhesion include sanding, scuffing, and the like. Chemical alterations include treatment of the substrate with compositions such as chromic acid conversion coatings, acid etch primers and the like.
Although such pretreatments have obtained improved refinish adhesion, they are undesirable for a number of reasons. Most importantly, pretreatments are inefficient and expensive to apply in terms of material, time, and/or labor costs. Some chemical pretreatments also present industrial hygiene and disposal issues. Finally, the use of some pretreatments such as acid etch primers may contribute to water sensitivity and/or coating failure under test conditions of extreme humidity.
Accordingly, it is highly desirable to eliminate the need for substrate pretreatment as regards the refinish coating of bare metal substrates.
In addition, adhesion to bare metal substrates is improved when the defect area to be repaired is relatively small and is surrounded by previously applied coating layers. Such previously applied coating layers act as an xe2x80x98adhesion anchorxe2x80x99 to the refinish coating. However, many refinish repairs are of a size such that they lack any surrounding adhesion anchors. Moreover, such anchoring adhesion may be completely absent when replacement body parts are painted with a refinish coating.
Another factor in formulating coatings is the volatile organic compounds (VOCs) that are released from the coating when it is applied. In solvent borne coating systems, there is a desire to reduce volatile organic compounds in order to comply with environmental requirements. One method of reducing VOCs is to use exempt solvents, which are solvents that are not calculated as a VOC emission.
One type of exempt solvent is parachlorobenzotrifluoride, which is sold under the trade name OXSOL(trademark) 100 by Occidental Chemical. One problem with using this type of solvent in a solvent borne system is that this solvent has a tendency to displace adhesional constituents, such as resin and anti-corrosive pigments, in the coating from the surface of bare metals. Without being limited to theory, it is theorized that the parachlorobenzotrifluoride has a low surface tension that operates to displace the other constituents in a coating composition. It would be desirable to improve the adhesion of solvent borne coating systems that contain parchlorobenzotrifluoride.
The present invention relates to a solvent borne coating composition comprising a resin, a polyether modified dimethylpolysiloxane, and parachlorobenzotrifluoride.
The present invention also relates to a method comprising applying the coating composition to a substrate and forming a coating.